(i) Field of the Invention
This invention relates to a rail anchoring system comprising a resilient rail anchoring clip and associated sleeper, which is suited to all classes of rail systems subjected to low axle loads (up to about 15 tonnes), medium axle loads (about 15 to 25 tonnes) and high axle loads (greater than about 25 tonnes). The clip is adapted, in use, to cooperate with the sleeper which has apertures formed through the upper surface thereof where, in use, a rail is to be positioned.
(ii) Description of Prior Art
Conventional resilient rail clips are sprung into position on either side of the foot of a rail by torsion or bending effects with one part of the clip bearing hard against the upper surface of the rail foot, another part of the clip being attached to the sleeper and bearing upwardly, whilst the final part of the clip bears down on the associated sleeper to balance the forces generated with the clip.
The effect of the above forces is to induce additional stress in the area of the sleeper, adjacent the rail, which can lead to failure of the sleeper.
Some types of such known clips are those manufactured by Pandrol Limited of Britain under the name of Pandrol (trade mark); Portec (Aust.) Pty. Ltd. under the name Sidewinder (trade mark); Omark (Australia) Limited under the name "Trak-Lok" (trade mark); and by B. V. Schroefboutenfabriek v.h. Everts en van der Weijden of Holland under the name D. E. Springclips.
All of the above known types of rail clips act to hold the rail foot against the sleeper against lifting forces and forces transverse of the rail direction, but in order to restrain the rail clip from moving longitudinally of the rail direction high toe loads (the loads applied on the upper surface of the rail foot) are necessary.
Other types of rail clips, commonly called rail anchors, are known and are formed in one piece to extend beneath the rail foot and engage on, or about, the edges of the rail foot, whilst bearing against the side faces of the sleeper. Such rail anchors act to restrain the rail against longitudinal movement, but additional hold-down clips or spikes are required to restrain the rail against lifting and transverse movements.
Steel sleepers also have a history of fatigue failure at the housings that locate the rail and/or clip and the rail seat areas.